Two questions are asked by this grant proposal. First, does herpes simplex virus (HSV) have genes, in addition to the gene for thymidine kinase (tk), which must function for the transformation of thymidine kinaseless L cells to a tk positive phenotype? And, second, what HSV antigens are expressed in transformed cells? We have shown that none of 7 cistrons with temperature sensitive defects is required for transformation. A mutant has been found that is conditional in its ability to transform on a high concentration of thymidine in the selection medium. Conditionally transformed cells could be super-transformed efficiently by wild type HSV indicating that HSV transformed cells do not contain immunity substances which limit sequential transfomation. We will continue to search for transformation defective mutants. HSV transformed cells express at least 3 HSV antigens. One antigen expressed is a structural component of the virion envelope. The antigen found in cells transformed by HSV-1 is present in HSV-1 but not HSV-2 virions and that found in cells transfomed by HSV-2 is present in HSV-2 but not HSV-1 virions. We will determine more fully which HSV antigens are expressed in transformed cells to learn the extent of HSV gene expression in transformed cells. BIBLIOGRAPHIC REFERENCES: Hughes, R.G., Jr., and W. H. Munyon. 1975. Transformation of thymidine kinaseless L-cells by temperature sensitive mutants of herpes simplex virus, type 1. Abstr. Ann. Meeting Am. Soc. Microbiol., S 322, p.267. Hughes, R.G., Jr., and W.H. Munyon. 1975. Temperature-sensitive mutants of herpes simplex virus type 1 defective in lysis but not in transformation. J. Virol. 16: 275-283.